The present invention relates generally to a system for fixation of two or more parts of a fractured bone. More specifically, the present invention relates to a bone implant and locking apparatus for internal fixation of a long bone, such as a femur.
Fractures commonly occur in the femur, and especially in the femoral neck and intertrochanteric regions. Traditionally, these fractures have been treated using a nail located in the femoral head in cooperation with a side plate located on the outside of the femur, or in cooperation with an intramedullary nail located in the intramedullary canal. The nail cooperates with the side plate or intramedullary nail to align and compress the bone fragments.
A high incidence of death is associated with hip fractures due to the injury itself or related complications. Frequent complications may arise when two or more bone fragments are forced towards each other when the patient supports his or her weight on the healing bone. For example, a sharp implanted nail or hip screw may cut through and penetrate the femoral head or neck; or a nail, hip screw, side plate, or intramedullary nail may bend or break under load where the contact between bone fragments is insufficient for the bone itself to carry the patient""s weight.
A variety of compressible fixation systems have been developed to maximize bone to bone contact while permitting bone fragments to migrate towards one another. For example, helical blades have been developed that may be inserted into and secured to the neck of a femur, and coupling mechanisms have been developed to slidably couple the helical blade to a side plate or intramedullary nail.
The prior art blades, however, may be susceptible to migration within the bone fragment and, even worse, may break free or pull out of the bone fragments, thus allowing the bone fragments to separate and/or become misaligned. Prior art blades are also susceptible to bending stresses, which may lead to undesirable bending or breakage of the blade.
In addition, many prior art coupling mechanisms provide unlimited amounts of sliding between the blade and the side plate or intramedullary nail, which may lead to disassembly of the blade and side plate/intramedullary nail. Furthermore, prior art coupling mechanism are often complicated and difficult to assemble during implantation.
Thus, a need exists for improved bone fixation systems.
The present invention is directed to bone fixation system including implants and coupling mechanisms for fixation of a bone. According to one aspect of the invention, an implant for fixation of a bone includes a shaft having proximal and distal ends and defines a longitudinal axis between the proximal and distal ends. A plurality of blades, each having proximal and distal ends, are disposed on the shaft and are helically twisted about the longitudinal axis. According to one embodiment, the plurality of blades may twist about 90xc2x0 around the longitudinal axis. At least one of the blades may have a variable blade width that varies along the longitudinal axis. For example, the variable blade width may increase in a direction from the blade proximal end toward the blade distal end. Additionally or alternatively, at least one of the blades may have a variable blade height that varies along the longitudinal axis. For example, the variable blade height may increase in a direction from the blade proximal end toward the blade distal end. The variable blade height is preferably substantially zero at the blade proximal end, such that the proximal end of the blade is substantially flush with the proximal end of the shaft.
According to a further aspect of the invention, the shaft of the implant may define a bladed portion and a non-bladed portion. The non-bladed portion may define a non-bladed diameter, and the bladed portion may define a bladed diameter that is smaller than the non-bladed diameter. In addition, the non-bladed portion may include a tapered region located substantially adjacent the bladed portion, wherein the tapered region defines a tapered region diameter that decreases in a direction toward the bladed portion. The tapered region may further define a neck diameter at a point substantially adjacent the blades that is smaller than the blade diameter.
The present invention is also directed to a coupling mechanism for coupling a first fracture fixation implant to a second fracture fixation implant. The coupling mechanism includes a body member receivable in the first implant and including a single prong extending from the body for contacting a surface of the second implant. The coupling mechanism further includes a drive member rotatably coupled to the body member for threadable engagement with the first implant. The drive member rotates freely with respect to the body member and may be used to urge the body member toward the second implant such that the single prong contacts the surface of the second implant and substantially prevents rotation of the second implant with respect to the first implant. More specifically, the single prong may define a first engagement surface, the second implant may define a second engagement surface, and the first and second engagement surfaces may interact to substantially prevent rotation of the second implant with respect to the first implant.
According to a further aspect of the invention, the single prong may limit sliding of the second implant with respect to the first implant. For example, the second engagement surface may include stops formed adjacent at least one of its ends for contacting the prong to prevent further sliding of the second implant.
The coupling mechanism may also be provided in a system for fixation of a fractured bone, which includes first and second fracture fixation implants.